The present invention relates generally to integrated circuit packages. More specifically, the invention relates to the clamping of lead frames during the manufacturing of a Leadless Leadframe Package.
An integrated circuit (IC) package encapsulates an IC chip (die) in a protective casing and may also provide power and signal distribution between the IC chip and an external printed circuit board (PCB). An IC package may use a metal lead frame to provide electrical paths for that distribution. During the process of die attach and wire bonding for conventional semiconductor packages, the semiconductor lead frame or substrate material rests on a base block during the epoxy dispensing, die attaching, and wire bonding processes. During these processes the frame or substrate needs to be held down firmly to a heater block by a vacuum, a clamp, or both.
To facilitate discussion, FIG. 1 is a top view of a lead frame panel 100 made up for a plurality of lead frames that may be used in the prior art. The lead frame may comprise leads 108, die attach pads 112, ties 116 for supporting the die attach pads 112 and leads 108, and a skirt 120 for supporting the plurality of leads 108 and ties 116. The lead frame panel 100 may be etched or stamped from a thin sheet of metal. FIG. 2 is a cross sectional view of the lead frame panel 100 shown in FIG. 1, along cut lines 2xe2x80x942, attached to a lead frame base tape 204, which is mounted on a base block 208 used in the prior art. The base block 208 has a plurality of holes 212, through which a vacuum is applied to the lead frame base tape 204 to hold the lead frame 100 and the lead frame base tape 204 to the base block 208. A top clamp 216 may also be used to hold the lead frame 100 and lead frame base tape 204 to the base block 208. Preferably, the holes 212 are positioned at the die attach pads 112, not between the die attach pads 112 and the ties 116 or at the ties 116. As a result, a base block with a configuration of holes for one type of lead frame may not be useful in clamping another type of lead frame.
FIG. 3 is a cross sectional view of another type of lead frame 300 mounted on the base block 208 that is used in FIG. 2. Tape 304 is placed across the leads, die attach pads 312, the ties 308, and skirt 320 of the lead frame 300. The tape 304 and lead frame 300 are placed on the base block 208. Two vacuum holes 212 are under parts of the tape 304 connected to die attach pads 312 and two vacuum holes 212 are under tape 304 that is next to a gap between a lead 308 and a die attach pad 312. Placing a lead 308 or gap over a vacuum hole 212 may cause the lead frame to float or bounce during the wire bonding process. As a result, the vacuum provided through the base block 208, even in combination with a clamping 316 may not be sufficient to secure the lead frame during the wire bonding and die attach process.
It is desirable to provide a universal base block that is able to secure different lead frame configurations.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a variety of techniques is provided for processing a lead frame. Generally, a first surface of a lead frame base tape is placed on a first surface of the lead frame. A second surface of the lead frame base tape is placed on a first surface of a porous block. A vacuum is placed on a second surface of the porous block.
Another aspect of the invention provides a device for processing lead frames, comprising a porous block with a first side and a second side, and a vacuum system connected to the first side of the porous block.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.